Homicide Help!

I'm building a program that is supposed to aid in homicide investigations by giving a possible profile of a killer, but I'm having trouble with the probability part. Here is a sample of the stats:

-80% of all murders in the US involving poison are committed by whites (so I'm saying that if the victim was poisoned, there is an 80% chance the killer was white)
-70% of all murders in the workplace are committed by whites (same as above)

lets say, for the sake of example, that a man was poisoned in the workplace. Are these two statistics independent? Can I obtain a probability that the killer was white based on this data? I believe that there should be a high chance of a white killer given the data, but I don't know how to express it mathematically. Thanks for any help you can give!!